A nitride semiconductor of the general formula InxGayAlzN (where x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1) has a band gap corresponding to blue light and ultraviolet light depending on its composition, and is utilized as a semiconductor light-emitting device such as a light-emitting diode (LED) or a laser diode (LD).
A semiconductor light-emitting device made of a nitride semiconductor generally has a semiconductor multilayer structure composed of a nitride semiconductor, electrodes for supplying a current for an active region of the semiconductor multilayer structure, and a substrate for supporting the semiconductor multilayer structure and the electrodes. Since a semiconductor multilayer structure is formed through epitaxial growth of a semiconductor layer on a substrate, the crystal quality of the semiconductor multilayer structure strongly depends on the substrate.
In order to perform an epitaxial growth of a nitride semiconductor layer having an excellent crystallinity, it is desirable that the underlying substrate is made of a gallium nitride (GaN). However, conventionally, it has been difficult to produce a GaN substrate, and therefore substrates of sapphire (Al2O3), silicon carbide (SiC), or the like have been used as substitutes.
However, in recent years, quality GaN substrates having a low dislocation density are becoming available, and further longevity of semiconductor light-emitting devices is being expected. Since a GaN substrate also has an excellent electrical conductivity, a semiconductor light-emitting device construction has been proposed in which a p-electrode is provided on the main surface side of the substrate and an n-electrode is provided on the rear surface side. By adopting such a construction, it becomes possible to downsize the semiconductor light-emitting device as compared to a construction where both of the p-electrode and the n-electrode are provided on the substrate main surface side. Therefore, it becomes possible to obtain a greater number of semiconductor light-emitting devices from a single wafer.
Generally speaking, a semiconductor light-emitting device in which a GaN substrate is used is fabricated by forming electrodes on both surfaces of the substrate and thereafter cleaving the wafer. In Patent Document 1, a method of patterning the n-type electrode in advance for exposing the region to split in order to facilitate this cleavage is proposed.
Moreover, it is necessary for an n-electrode which is provided on the substrate rear surface side to form a good ohmic contact with the substrate and to adhere strongly to the substrate. In Patent Document 2, in order to satisfy such requirements, a semiconductor light-emitting device having an n-type electrode with a 3-layer structure is proposed.
In Patent Document 3, a method is proposed in which an edge scribing is performed from the p-type nitride semiconductor layer side and thereafter a cleavage is performed via breaking, in order to obtain a good cavity end face which is mirror-finished.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 11-340571    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2002-26443    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2000-58972